One major use for single-phase asynchronous induction motors is for the circulation of cooling air on and around heat exchange surfaces. The various types of asynchronous induction motors used for such purposes, as well as other purposes, include distributed wound and half-pitch capacitor induction motors as described in U.S. Pat. No. 4,371,802. Because these motors are capable of running only at one speed for a given load, the industry currently sizes the motors for worst case conditions. For example, where such a motor is used in a refrigerator as a fan motor for circulating air around the heat exchange surfaces, refrigeration manufacturers size the fan motor for the most extreme combination of heat dissipation conditions. In view of this, the fan motor operates at all times as if a worst case condition exists. Accordingly, power consumption is correspondingly always high and the noise created by the fan motor is also correspondingly high.
In view of the foregoing, there is a need for varying the rotational speed of asynchronous induction motors so that the quantity of circulating cooling air in refrigerators and other appliances can be varied with need and so that power consumption of the motor can be decreased correspondingly with need.
Although various means have previously been introduced for varying the speed of asynchronous induction motors, however, such means have been generally expensive and, on occasion unreliable, especially when the induction motor must operate for a period such as 10 to 20 years.
Accordingly, it is the object of this invention to provide an asynchronous variable speed induction motor for use in appliances, such as refrigerators, clothes dryers, hair dryers, etc. It is further the object of this invention to provide a variable speed induction motor that is generally reliable, generally inexpensive to manufacture, and wherein the power consumption decreases as the speed of the motor decreases.